1. Field of the Invention
The present invention relates to a bubble-removing apparatus, and more particularly to an apparatus for removing bubbles entrained in a liquid such as industrial water, oil and chemical solutions.
2. Background Information
Various fluids are used for various purposes. In such use, inconvenience is often caused when bubbles are entrained in the fluids. For example, during a cleaning step of a semiconductor production process, a cleaning solution consisting of acid-based chemicals or alkaline-based chemicals contained in a constant mixing ratio is circulated in a cleaning bath in a predetermined amount to conduct automatic cleaning of semiconductor substrates. In this case, in order to realize the cleaning effects with good stability and reproducibility, it is important to maintain a constant mixing ratio of chemicals, and for this purpose, a stable supply of chemicals in a predetermined amount is required. The bubbles entrained in a liquid of the kind described must be removed therefrom because they cause damage to equipment, increase compressibility of the liquid, cause vibration and noise, result in poor product quality, and cause deterioration and change in the quality of the liquid.
Various methods have been used for measuring a supplied amount of a cleaning solution which is supplied automatically. Recently, an ultrasonic flow meter having the advantages of facilitating miniaturization of a measurement apparatus and varying pressure has been widely used. This ultrasonic flow meter has the further advantage that the supplied amount of cleaning solution can be readily changed and the mixing ratio of chemicals can thereby be simply adjusted automatically. However, the ultrasonic flow meter is susceptible to the influence of bubbles in the cleaning solution, and accurate measurement can not be made without eliminating the bubbles. These bubbles are formed, for example, during a change of canisters containing chemicals or during operation of the pump (e.g., a diaphragm pump). For this reason, various types of conventional bubble-removing apparatuses have been proposed and employed. However, in many cases, when bubbles are discharged, the solution is entrained in the bubbles and are both discharged together in a large amount. Furthermore, with such conventional bubble-removing apparatuses, additional equipment, such as a suction pump or a tank, must be provided to insure proper liquid/gas separation and subsequent discharge of the gas, thereby increasing the overall size of the apparatus. Accordingly, an operation where only a small amount of cleaning solution is discharged can not be achieved.
A bubble-removing apparatus has been known in which a liquid is fluidized by mixing it (e.g., by rotation) in a vessel and the bubbles are collected at the central portion for removal in order to use the apparatus even when the flow amount is small. For example, one such apparatus is disclosed in JP-A-11-19406. According to the disclosure in JP-A-11-19406, the bubble-removing apparatus can be used even in a case where the flow amount of liquid is low, and the apparatus is constructed to separate bubbles and collect the bubbles towards the central axis of a vessel by a rotating flow and to discharge the bubbles through a discharge outlet provided at the central axis of the vessel. At the discharge outlet of this apparatus, an automatic ON-OFF valve is disposed. The ON-OFF valve has a mechanism wherein a spherical discharge valve float is raised by the buoyancy of the liquid to shut the discharge outlet, and when bubbles are collected, the discharge valve float is released by its own weight and a spring to discharge the bubbles through the outlet.
However, in the case of the automatic ON-OFF valve of the abovementioned apparatus, since it is necessary to use the spring to securely open the discharge outlet when the liquid comprises chemicals such as acid or alkali, it is difficult to maintain a stable performance for a long period of time. Further, operation of the valve varies depending upon the balance of, for example, the discharge valve float""s own weight, the spring force of the spring and the buoyancy of the discharge valve float. Accordingly, when the internal pressure inside the vessel largely changes by the flow amount of the liquid which flows into the vessel, the operation of the valve can not accurately follow the change. For this reason, with such type of apparatus alone, it has not been possible to treat a liquid which is to be used for the case where the flow amount is widely varied.
A bubble-removing apparatus has been known wherein an air vent which has a ball element instead of a spring is disposed at the discharge outlet. However, in such apparatus, the ball element is unstable, and when the flow amount increases, the ball element will float in the air vent and the liquid will flow out together with the bubbles. Further, when the ball element is raised and shuts the discharge outlet of the air vent, the liquid containing bubbles will flow out from the outflow port of the bubble-removing apparatus, thereby preventing the removal of bubbles. In addition, since the ball element has a spherical surface, when the ball element moves only a little, the liquid flows into the air vent and the air vent becomes filled with the liquid, whereby the ball is made further unstable and it becomes difficult to keep balance with the flow amount.
Further, a pump is used in order to permit the liquid to flow into a cleaning bath or the like through the above bubble removing apparatus. Usually, however, the pump does not necessarily create a constant pressure at all times. Particularly, with diaphragm pumps, air-actuated pumps and the like, the pressure can not be kept constant and pulsations are generated, whereby the flow amount becomes unstable due to transfer of such pulsations. As a result, problems may sometimes arise when the above liquid is used, for example, in a subsequent cleaning step.
It is an object of the present invention to provide a bubble-removing apparatus for removing bubbles entrained in a fluid regardless of the flow amount of fluid or a fluctuation in the flow amount.
Another object of the present invention is to provide a bubble-removing apparatus by which bubbles entrained in a fluid can be removed from a bubble discharge outlet without permitting the fluid to flow out from the discharge outlet.
Another object of the present invention is to provide a bubble-removing apparatus which does not require additional equipment, such as a suction pump or a tank, for the effective removal of bubbles from a liquid and the subsequent discharge of the bubbles.
Still a further object of the present invention is to provide a bubble-removing apparatus by which the internal pressure can be controlled and by which pulsations of fluid flowing out from a discharge outlet can be buffered while bubbles are removed from the fluid.
The foregoing and other objects of the present invention are carried out by a bubble-removing apparatus comprising a main body having a main chamber comprised of a first chamber portion, a second chamber portion and a third chamber portion connecting the first chamber portion in fluid communication with the second chamber portion. A stationary rod or bar is disposed in the main chamber along a central axis thereof. At least one inflow port is disposed in the main body for introducing a fluid containing entrained bubbles tangentially into the main chamber so that the fluid is caused to rotate in the first, second and third chamber portions about the central axis of the main chamber to thereby cause the bubbles to separate from the fluid and collect around the bar.
The main body has an outflow port for discharging the fluid whose entrained bubbles have been separated, and a discharge outlet for discharging the bubbles separated from the fluid. A valve chamber is disposed between the discharge outlet and the first chamber portion of the main chamber. A block member is disposed in the valve chamber and has a through-hole in fluid communication with the first chamber portion of the main chamber. A float member is disposed in the valve chamber for undergoing movement therein relative to the block member. The float member is disposed over the block member so that a first gap is formed between an outer surface of the block member and an inner surface of the float member, and a second gap is formed between an outer surface of the float member and an inner surface of the valve chamber. The float member undergoes movement within the valve chamber in response to an increase in internal pressure within the main chamber during rotation of the fluid and separation of the bubbles from the fluid. Movement of the float member within the valve chamber places the through-hole of the block member into and out of fluid communication with the discharge outlet through the first and second gaps to thereby control discharge of the bubbles through the discharge outlet.
Preferably, the first and third chamber portions are generally cylindrical-shaped and the second chamber portion has a generally inverted conical shape. A diameter of the first chamber portion is preferably greater than that of the third chamber portion.
The block member is preferably cylindrical shaped and is integral with a substrate for engaging an upper end of the first chamber portion. The float member preferably comprises a cylindrical wall surrounding the block member and an upper plate closing an upper end of the cylindrical wall. During movement of the float member within the valve chamber, the upper plate of the float member opens and closes an open end of the through-hole of the block member to place the discharge outlet into and out of fluid communication with the first chamber portion of the main chamber through the first and second gaps.
In one embodiment, a ring member is disposed in the valve chamber between the outer surface of the float member and an inner surface of the valve chamber so that the second gap is disposed between the outer surface of the float member and an inner surface of the ring member, and a third gap is formed between an outer surface of the ring member and the inner surface of the valve chamber. The ring member undergoes movement within the valve chamber in response to a change in internal pressure in the second gap.
The cylindrical wall of the float member has an inner diameter greater than an outer diameter of the block member so that the first gap is formed between the outer surface of the block member and the inner surface of the float member. The width of each of the first, second and third gaps in the diametrical direction thereof is selected so that the bubbles separated from the fluid can efficiently pass therethrough while substantially preventing the fluid from which the entrained bubbles have been separated from passing therethrough. Preferably, the dimension of the gaps is from about 0.05 mm to 0.3 mm, and more preferably from about 0.1 mm to 0.2 mm, when the fluid containing entrained bubbles comprises a water-type fluid. When the fluid containing entrained bubbles comprises an oil-type fluid, the dimension of the gap is preferably from about 0.2 mm to 1 mm, and more preferably from about 0.5 mm to 0.8 mm.
The range of movement of the float member within the valve chamber is limited by the distance between an upper surface portion of the block member and an inner upper surface of the valve chamber. When fluid does not enter the through-hole of the block member from the first chamber portion of the main chamber, a lower surface of the upper plate of the float member abuts the upper surface portion of the block member to close the open end of the through-hole of the block member. When fluid enters the through-hole of the block member, pressure generated by the fluid causes the float member to move away from the block member to open the open end of the through-hole of the block member and place the discharge outlet in fluid communication with the first chamber portion of the main chamber through the gaps. When the pressure generated by the fluid is sufficiently high, the float member is caused to move away from the block member until an upper surface of the upper plate of the float member abuts the inner upper surface of the valve chamber and closes the discharge outlet. The distance between the upper surface portion of the block member and the inner upper surface of the valve chamber is selected so that when the upper surface of the upper plate of the float member abuts the inner upper surface of the valve chamber, the float member does not come away from the block member (i.e., the float member remains positioned over the block member).
According to the present invention, in a condition in which the pressure generated by the fluid is sufficient to cause the float to move away from the block member but not sufficient to bring the upper surface of the upper plate of the float member into abutment with the inner upper surface of the valve chamber, only the bubbles separated from the fluid are permitted to pass through the gaps and discharged through the discharge outlet. The range of movement of the float member in this condition is preferably from 1 mm to 5 mm, and more preferably 1 mm to 3 mm, measured from the inner upper surface of the valve chamber and the upper surface of the upper plate of the float member.